The present invention relates to ophthalmic lenses employed in connection with ophthalmic diagnostic and surgical procedures and, more particularly, to a compound ophthalmic lens that is utilized for observation of the fundus, and particularly the peripheral retina of the eye, and for delivery of laser energy thereto.
Opthalmic lense are conventionally utilized for observation of various locations within the eye by ophthalmologists. These ophthalmic lenses normally include a contact lens, that is, a lens that directly contacts the cornea of the eye and may include an entry lens that is spaced in the anterior direction from the contact lens. The entry lens usually magnifies that portion of the eye being observed. The two lenses are normally joined by a housing. Mirrors are sometimes interposed between the contact lens and the entry lens to increase the field that can be viewed by the physicain through the lens.
Most ophthalmic lenses of the type just described have been created and designed for use as an observation tool utilized in conjunction with a slit lamp or ophthalmic microscope employed by ophthalmologists. While most prior lenses function reasonably well for use as an observation tool, the advent of laser microsurgery and the accompanying need to deliver a laser beam safely within the eye has created a need for ophthalmic lenses that not only provide improved images of the desired location in the eye but also have the capability to deliver laser energy to the desired location with minimum effect on other portions of the eye.
One example of the use of laser energy is in connection with the treatment of a patient's fundus. This treatment requires not only the capability to observe the fundus over a wide angle but the capability of being able to deliver a laser beam within the eye and focus it on the fundus. One lens currently available for wide-field fundus observation has at least three elements. Some of these elements are cemented together such that it is effectively a two lens system. The lens forms a real image within the final lens element. While the fundus image so created is adequate, axial magnification is poor, and the internal and external reflections caused by the various lens elements degrades the overall image available and reduces fundus detail if the ocular media is hazy. Moreover, the prior lens exhibits aberrations around the peripheral portion of the image and laser delivery to the peripheral retina is adversely affected by beam astigmatism induced by the lens.
A significantly improved lens is disclosed in U.S. Pat. No. 4,728,183. That lens uses an aspheric entry lens to produce an aerial image spaced from and anterior of the entry lens. The combination of the contact lens and the aspheric lens produces an aerial image that has very high resolution, even in the peripheral areas of the image. The lens also produces very little reflected or scattered light as well as a nondistorting path through which the laser beam can pass during treatment of a patient's pathology. The lens disclosed in this patent also maintains a wide cone angle on the laser beam as it passes through the patient's cornea and crystalline lens to minimize energy absorption in those elements of the patient's eye.
The lens disclosed in U.S. Pat. No. 4,728,183, however, has certain drawbacks even though it produces a superior optical image. First, the field of view is limited generally to the central and mid-peripheral fundus and, upon manipulation of the lens, to areas of the retina approaching the equator. It is desirable to increase the field of view of the lens so that the peripheral retina in the region of the equator and slightly beyond can be viewed. This increased field of view is desirable not only for delivery of laser energy for treatment of retinal detachment in the peripheral area but also for other procedures such as panretinal photocoagulation. One suggestion for increasing the field of view is to merely increase the power of the contact lens. However, the greater curvature of the anterior surface of the lens required to increase the field would greatly increase the aberrations in peripheral regions of the aerial image and thus make it unacceptable for use in diagnosis and laser delivery. Additionally, the lens disclosed in U.S. Pat. No. 4,728,183 produces an aerial image some 12 mm from the anterior surface of the entry lens. The distance between the aerial image and the patient's eye makes this lens unusable with some slit lamps employed by physicians. It is therefore desirable to reduce the distance between the aerial image and the patient's eye to provide a lens that is universally compatible with modern slit lamp microscopes.